Apparatus for the measurement of the mass of a flowing medium

ABSTRACT

An apparatus for the measurement of the mass of a flowing medium, such as for the measurement of the induced air mass in internal combustion engines which includes at least one temperature-dependent resistor film disposed in the flow of the medium, the temperature and/or resistance of the film being governed in accordance with the mass of the medium wherein the manipulated variable is a standard for the mass of the medium. The temperature-dependent resistor film is disposed in a region of stabilized flow in the flow cross section and, to this end, the temperature-dependent resistor film may be disposed either upstream of the narrowest cross section of a nozzle-like constriction wherein the pressure steadily decreases or in a gap having a laminar gap flow.

CROSS REFERENCE TO COPENDING APPLICATION

Of interest only is a copending application of Werner Grunwald et al.,Ser. No. 96,071 filed Nov. 20, 1979 (Group 244) owned by the sameassignee.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for the measurement of the mass ofa flowing medium. An apparatus is already known for the measurement ofthe mass of a flowing medium in which a film resistor placed upon acarrier is used as the temperature-dependent resistor. In itsapplication, the apparatus is also used in a Reynolds-number range inwhich a very unstable, laminar flow predominates. Laminar flowseparations appear continuously in this situation which vary theheat-transfer coefficient and thus the measurement signal of theapparatus. However, a sharply fluctuating measurement signal isunsuitable for control purposes.

OBJECT AND SUMMARY OF THE INVENTION

The apparatus according to the invention has the advantage over theprior art that through the disposition of the temperature-dependentresistor film in a region of stabilized flow, a measurement signal isobtained which is smooth and as precise as possible.

It is particularly advantageous to place the temperature-dependentresistor in the region of a nozzle-like constriction in which a constantpressure reduction is assured in the direction of flow.

It is also advantageous to dispose the temperature-dependent resistorfilm in at least one narrow gap having a laminar gap flow.

The invention will be better understood as well as further objects andadvantages thereof become more apparent from the ensuing detaileddescription of the preferred embodiments taken in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a basic circuit for an apparatus usedto measure the mass of a flowing medium with the use of atemperature-resistant resistor;

FIG. 2 is a sectional view of a flow cross section of one embodiment ofa temperature-resistant film resistor in a nozzle-like constrictionconstructed in accordance with the invention;

FIG. 3 is a view similar to FIG. 2 of another embodiment of thetemperature-dependent resistor of the invention;

FIG. 4 is a view similar to FIG. 2 of a third embodiment of thetemperature-dependent resistor of the invention;

FIG. 5 is a sectional view of a temperature-resistant film resistor inat least one gap having a laminar gap flow constructed in accordancewith the invention; and

FIG. 6 is a view similar to FIG. 5 showing another embodiment of thetemperature-resistant film resistor in at least one gap having a laminargap flow constructed in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is shown an intake manifold 1 of aninternal combustion engine (which is not further illustrated), intowhich the air induced by the engine flows in the direction indicated bythe arrows 2. A temperature-dependent resistor 3, such as a hot-filmresistor, is located in the intake manifold 1 and is subjected to theoutput value of a controller and simultaneously furnishes the inputvalue for the controller. The temperature of the temperature-dependentresistor 3 is controlled to a fixed value which is above the average airtemperature. If the flow velocity--that is, the quantity of air inducedper unit of time--increases, then the temperature-dependent resistor 3cools to a greater extent. This cooling is fed back to the input of thecontroller, so that the controller increases its output value in such amanner that the set temperature value is again established at thetemperature-dependent resistor 3.

The output value of the controller governs the temperature of thetemperature-dependent resistor 3, in accordance with variations in theinduced air quantity, to the predetermined value and simultaneouslyrepresents a standard for the induced air quantity, which is deliveredas a measurement value to a metering circuit in order to adapt therequired quantity of fuel to the quantity of air induced per unit oftime.

The temperature-dependent resistor 3, together with a resistor 4,comprises a first bridge arm, which has a second bridge arm connectedparallel therewith comprising the two fixed resistors 5 and 6. Betweenthe resistors 3 and 4, there is the pickup point 7, while the pickuppoint 8 is located between the resistors 5 and 6. The two bridge armsare connected in parallel at points 9 and 10.

The diagonal voltage of the bridge appearing between points 7 and 8 isapplied to the input of an amplifier 11 having output terminals to whichthe points 9 and 10 are connected, so that the output value of theamplifier 11 supplies the bridge with operational voltage or operationalcurrent. The output value, designated from henceforth as the manipulatedvariable U_(S) controls the metering of the fuel required for theinduced air in a fuel metering circuit, (not illustrated) of the engine.

The temperature-dependent resistor 3 is heated up by the air flowpassing through it, up to a value at which the input voltage of theamplifier 11, that is, the bridge diagonal voltage, becomes zero orassumes a predetermined value. From the output of the amplifier 11, aspecific current flows into the bridge circuit. If the temperature ofthe temperature-dependent resistor 3 varies as a result of a variationin quantity of the induced air, then the voltage varies at the bridgediagonal, and the amplifier 11 governs the bridge supply voltage or thebridge current to a value for which the bridge is again balanced or isout of balance in a predetermined manner.

The output value of the amplifier 11, the control voltage U_(S), thusrepresents a standard for the induced air quantity, just as does thecurrent in the temperature-dependent resistor 3.

In order to compensate for the influence of the temperature of theinduced air on the measurement results, it may be advantageous toinclude a second resistor 14, surrounded by a flow of induced air, inthe second bridge arm. In so doing, the dimension of the resistors 5, 6and 14 must be chosen such that the output loss of thetemperature-dependent resistor 14, which is generated by the bridge armcurrent flowing through it, is so small that the temperature of thisresistor 14 does not vary practically with the variations in the bridgevoltage, but rather always corresponds to the temperature of the inducedair flowing past it.

As is shown in FIG. 2, the temperature-dependent resistor 3 may beformed as a resistor film, which is placed upon a carrier 17 inaccordance with any known process. If the carrier 17 is made of anelectrically conductive material, then an insulating layer is providedbetween the resistor film 3 and the carrier 17. A nozzle body 18 isdisposed in the flow cross section 1. This nozzle body 18 need notdefine the entire flow cross section but instead may also, as shown inFIG. 5, include only a portion of the flow of the medium.

Upstream of the narrowest cross section 19 of the nozzle body 18, in theembodiment of FIG. 2, the carrier 17 is disposed along with thetemperature-dependent film resistor 3. The carrier 17 is formed, by wayof example, as lenticular in shape. In other words, it is so formed thatbetween the wall 20 of the nozzle-like constriction of the nozzle body18 and the carrier 17, the resultant flow cross section narrows steadilyin the direction of the flow. The pressure which thus also steadilydecreases in the direction of flow toward the narrowest cross section 19causes the boundary layer profile to be convex in shape and without anyunsteadiness; i.e., no laminar flow separations appear. If the pressurewere to rise in the flow direction instead, the boundary layer profilewould have a turning point and a smaller velocity increase in thevicinity of the wall which would cause laminar separations that wouldappear irregularly both in time and in location.

The disposition of the carrier 17 with the temperature-dependentresistor 3 in the nozzle-like constriction of the nozzle body 18, inaccordance with the invention, thus brings a stabilization of the flow,as a result of which a measurement signal can be obtained which issmoother and more precise.

In the embodiment of FIG. 4, the temperature-dependent film resistor 3is applied directly to the wall 20 upstream of the narrowest crosssection 19 of the nozzle-like constriction of the nozzle body 18. Thenozzle body 18 thus serves simultaneously as the carrier of the resistorfilm 3. Because of the disposition of the temperature-dependent resistorfilm 3 pointing exclusively upstream on the nozzle body 18, theappearance of flow separations is prevented because of the steadyreduction in pressure.

If there is a variation in the flow velocity and thus a change in theheat-transfer coefficient, the temperature distribution in the nozzlebody 18 varies. The time which transpires until the new status isreached depends upon the heat capacity of the nozzle body 18. By meansof a suitable selection of the mass and the surface area of the nozzlebody 18, a desired damping of the measurement signal of the apparatusfor the measurement of the mass of the flowing medium can be determinedbeforehand.

Further possibilities for stabilizing the flow are shown in theexemplary embodiments of FIGS. 5 and 6. In FIG. 5, a controlled-gap body23 having minimum flow resistance is disposed in the flow cross section1 via a rib 22. This body 23 has a narrow gap 24 parallel to the flowand extending in the flow direction and a laminar gap flow prevails ingap 24 without separations. The carrier 17, having thetemperature-dependent resistor film applied on all sides, may beplate-like and disposed within the gap 24 in such a manner that gapportions 25 and 26 result on either side of the carrier 17 within eachof which there is a laminar gap flow.

In the embodiment shown in FIG. 6, a controlled-gap body 23 having a gap24 producing a laminar gap flow is similarly provided. However, in theembodiment of FIG. 6, the temperature-dependent resistor film 3 isplaced upon the surface of the controlled gap body 23 defining the gap24 so that the controlled-gap body 23 simultaneously acts as the carrierfor the temperature-dependent resistor film 3.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other embodiments and variantsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. Apparatus for the measurement of the mass of aflowing medium such as for the measurement of induced air mass ininternal combustion engines comprisingan intake manifold having a nozzlebody disposed in at least a portion of the flowing medium thereof, acarrier disposed upstream of a narrowest cross-section of said nozzlebody, a hot-film, temperature dependent resistor applied upon saidcarrier and in a path of said flowing medium defining a region ofstabilized flowing medium, said resistor having at least one of thetemperature and resistance characteristics of the flowing medium fordeveloping thereby a measurement signal indicative thereof.
 2. Theinvention of claim 1 wherein said nozzle body includes an inner wall forproducing a resultant flow cross-section which narrows steadily alongthe direction of flow.
 3. The invention of claim 2 wherein said nozzlebody has an inner surface which narrows in a manner of a nozzle andwherein said temperature-dependent resistor is applied to said innersurface.
 4. The invention of claim 1 wherein said carrier is integrallyconstructed with said nozzle body and said resistor is applied upon saidnozzle body.
 5. The invention of claim 1 wherein said resistor comprisesan arm of a bridge circuit and which has a second arm parallel to saidarm, an output of said bridge being said measurement signal applied asan input to an amplifier providing an output valve applied to saidbridge circuit.